This invention relates to a method and apparatus for the processing of liquids to reduce microbial and/or enzymatic activity therein and, more particularly, to the use of carbon dioxide to achieve reductions of microbial and/or enzymatic activity.
There are many methods for improving the shelf life of liquid products such as orange juice, apple juice, milk, latex paints, peanut butter, soup, etc.
Commercially, thermal methods such as pasteurization are the predominant methods used to improve the shelf life of liquid foods. Ultra-high pressure treatment is also used for liquid foods, but less frequently.
In high pressure treatment facilities, fluids containing microbial contamination are pressurized hydrostatically to kill the majority of the bacteria. In such systems, pressures are created which equal or exceed 30,000 psia and commonly range from 60,000 to 120,000 psia. Such hydrostatic treatment, however, is unsafe because of the very high pressures, is a lengthy process, is batch rather than continuous, and is expensive due to the high capital costs of the required equipment.
Other methods for shelf-life extension of liquids include nuclear irradiation, ultra-violet exposure and application of microwaves. These treatments are expensive and not widely used commercially at present.
High pressure homogenization has been used to increase the shelf life of orange juice and other single-strength citrus juices as described in U.S. Pat. No. 5,232,726 to Clark et al. It is disclosed that a citrus juice being processed is subjected to a high pressure of about 15,000 psia, with the result being a significant reduction in biological activity in the juice.
Carbon dioxide has been used to inactivate enzymes in food and reduce microbial populations in fruit juices as described in U.S. Pat. No. 5,393,547 to Balaban et al. Balaban et al. describe a method for inactivating enzymes in liquid food products wherein the food is exposed to pressurized carbon dioxide which, in turn, produces a carbonic acid solution with a pH that is sufficiently low to irreversibly inactivate enzymes in the liquid food. The Balaban et al. method is indicated as being applicable to either batch mode or continuous flow mode processing of food. Balaban et al. further indicate that supercritical carbon dioxide is introduced at a rate sufficient to allow enough thereof to dissolve in the food to inactivate the enzymes. After enzymatic inactivation, the food flows to a section where pressure is reduced and the released carbon dioxide may be recycled for repeat usage.
U.S. Pat. No. 5,704,276 to Osajima et al. describes a method for continuous deactivation of enzymes in liquid foodstuffs, using a supercritical form of carbon dioxide. Osajima et al. indicate that the density of the supercritical fluid is less than that of the liquid food and that the supercritical carbon dioxide is injected continuously into the liquid food and is separated therefrom in a later stage of the process. Osajima et al. also indicate that their process deodorizes the liquid food and removes volatile components.
Arreola et al. in xe2x80x9cEffect of Supercritical Carbon Dioxide on Microbial Populations in Single Strength Orange Juicexe2x80x9d, Journal of Food Quality, Volume 14 (1991), pp. 275-284, describe the effect of supercritical carbon dioxide on microbial populations in orange juice. Using a batch process, Arreola et al. concluded that high pressure carbon dioxide treatment resulted in microbial reduction in single strength orange juice, even at low temperatures. Further, they conclude that a combination of high pressure, and shear forces to which the orange juice is subjected during depressurization and lower pH due to temporary formation of carbonic acid may have further inhibitory effects on the normal flora within orange juice. During the processing described in this paper, the minimum temperature utilized was 35xc2x0 C.
It is an object of this invention to provide an improved method and apparatus for reducing microbial and/or enzymatic activity in liquid products.
It is a further object of this invention to provide a method and apparatus for reducing microbial and/or enzymatic activity in liquid products using pressurized carbon dioxide, wherein the processing temperature to which the liquid is subjected does not deleteriously affect the liquid products.
It is yet another object of this invention to provide a continuous flow method and apparatus for reducing microbial and/or enzymatic activity in liquid products using pressurized carbon dioxide.
A continuous method using a pressurized flow of carbon dioxide is described for the reduction of microorganisms present in the liquid product and/or the inactivation of one or more enzymes in a pressurized flow of the liquid product. In one embodiment, the pressure in the flow regions is maintained at a level which is sufficient to keep the carbon dioxide in dense phase, but at a temperature which does not freeze the liquid product. In another embodiment, gaseous carbon dioxide is injected directly into the liquid product, forming a mixture which is thereafter pressurized.
The pressurized mixture of the carbon dioxide and liquid flows through a reaction zone for a sufficient time to reduce harmful microorganisms and inactivate enzymes and then enters one or a plurality of expansion stages wherein the pressure of the mixture flow is decreased sufficiently to allow the separation of carbon dioxide from the liquid product. Heat is applied if necessary, to the extent necessary, in at least some of the expansion stages to prevent a cooling of the mixture flow to the freezing point of the liquid product. If heat is applied, the temperature should preferably be controlled so that the liquid does not exceed a temperature at which deleterious effects are experienced. (Freezing and excessive high temperature can have negative effects on the juice quality. Temperatures over 40xc2x0 C. begin to degrade the product.)
The present invention is contemplated for use with any fluid that may be transported through a conduit, including for example, beverage products such as juices and milk, semi-liquid foods such as mayonnaise, salad dressings, soup and cottage cheese, and other fluids such as paint and sterile injectibles.